Tilapia

The Tilapia fish is an exotic invasive species introduced in Australia in the seventies, which is taking hold in Queensland rivers. Anja Taylor investigates new DNA technology which detects Tilapia in waterways. This research may help prevent devastating infestations from occurring.

TRANSCRIPT

NARRATIONThe devastating problem created by this rather unremarkable-looking fish began in a tank like this. Tilapia were popular as tropical aquarium fish until they were banned in the 1970s.

Dr Damien BurrowsAuthorities realised that these fish could pose a threat to the native environment of Australia so they made them illegal.

NARRATIONIronically, this move may have led to the mass deliberate release of tilapia into Australian ponds, creeks and rivers.

Dr Damien BurrowsAnd since then, they've been slowly spreading to other catchments and they are the most serious aquatic pest that we have here in Queensland.

NARRATIONToday, tilapia have become so abundant, they're often referred to as the cane toad of the waterways. But because they lurk below the surface, by the time they're detected it's often too late to eradicate them.

Dr Damien BurrowsOnce they get truly established it is impossible. And there are creeks around here where all you catch is tilapia.

NARRATIONNow an astonishingly quick new way to find tilapia without even sighting them promises not only to help stop the spread of this pest species but it may also revolutionise how we investigate life underwater. It's too late for the Ross River in Townsville. This river has more invasive fish species than any other river in Australia.

Anja TaylorThe river is in an urban area, the weather is tropical and the water is warm. So it's a lovely home for tropical aquarium fish. At the last count, this river had 20 species of exotic fish in it. Today we're out to find tilapia by electrofishing.

NARRATIONOur rubber waders are protecting us from the electrical current that's coming from Dr Damien Burrows' backpack and into the water around us.

Dr Damien Burrows..which comes through the wand here and is emanated at that ring. It stuns all fish within about a metre or so radius and it doesn't kill them, just immobilises them so we can catch them in the net.

Anja TaylorSo there's lots of tilapia in here?

Dr Damien BurrowsThere are plenty of tilapia in here, yes.

Anja TaylorOK.

Dr Damien BurrowsWe'll get one in a moment.

Anja TaylorAlright, I got one.

Dr Damien BurrowsGot him?

Anja TaylorOh, he's big!

Dr Damien BurrowsThat's a Mozambique Mouthbrooder. They come from Africa. These fish are incredibly good at building really large numbers. They can survive in poor water quality. They're very aggressive, so basically you end up with a really large population of aggressive fish living in our creeks, which actually out-compete and chase away our natives.

NARRATIONTilapia can tolerate a wide range of temperatures, put up with high salinities and low levels of oxygen.

Dr Damien BurrowsThey were originally thought to be herbivores but our research has shown that they'll actually quite readily consume native fishes, including barramundi.

NARRATIONDamian's main goal is to get to the front line of tilapia invasions before they take hold. And that's meant countless frustrating days looking in all the wrong places.

Dr Damien BurrowsTypically we'd actually have to take a boat and use nets. Or we can use traps, or we can apply electricity to the water, which is our favoured technique. And you might go to a waterhole at considerable expense and not find them. It doesn't mean they're not there, it just means they're low abundance and you haven't found them.

Anja TaylorNow detecting tilapia has become much easier. In fact, surveying a field site is as simple as this. Every bit of information about what lives in this waterway is contained here in this bottle.

NARRATIONYou might not see anything, but this water is brimming with DNA. As tilapia go about their daily business, they shed cells in their mucus, scales and faeces, and each of those cells contains DNA.

Heather Robson PhD studentHi, did you get some more?

Dr Dean JerryHopefully all full of tilapia DNA.

NARRATIONAquatic geneticist Dr Dean Jerry and his team have developed a technique which can extract and identify DNA from all species of tilapia in a water body just days after they arrive.

Dr Dean JerryIt's actually very simple. All we do is we filter the water and the vacuum pump essentially draws the water through that filter membrane and any cells or any biological material that is in that water will get trapped on the filter membrane.

NARRATIONBack in the lab, DNA is extracted by dissolving the cells on the membrane into solution. A primer is added that amplifies only tilapia DNA, and it's run through a standard polymerase chain reaction, ending in a positive or negative result.

Dr Dean JerrySo you see here, wherever we have the band, that is where we have tilapia DNA. And so you can see we've got tilapia present in the Ross River, in Lake Eacham, Tinaroo...

Anja TaylorCan you tell how many tilapia are in each place?

Dr Dean JerrySo where we have the brighter bands usually means there's lots of DNA, whereas in other regions where the DNA band isn't quite as bright it means that we don't have as much DNA in our reaction. So it allows us to detect where there's only a few individuals in a water system and therefore, where you have those few individuals, that's usually the invasion front - tilapia have only just colonised those waters. It's a type of tool that we can go out into the field very quickly, sample large numbers of water bodies very cheaply.

Dr Damien BurrowsThat's a revolution for me. That's certainly going to turn the way we do things upside down, but for the good, it's a positive revolution for us.

NARRATIONBut there's no reason to stop at tilapia. The potential for using the e-DNA technique as a survey tool is virtually limitless.

Dr Dean JerryConceivably, when we take a water sample, in that water sample, if there are cells from all the organisms that are in that water system, we should be able to extract the DNA and detect them. So this is the holy grail, I guess, for an ecological geneticist.

Dr Damien BurrowsIt'll only be a few years away, I think, where we'll be to the point where we can take a single sample of water and work out all the native fishes, all the pest species, the turtles, the crayfish, the crabs, frogs - everything - from one water sample. It is certainly the most promising game-changing technology that I've seen in my 20-plus years as a freshwater ecologist, yes.

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YOUR COMMENTS

"Aquatic geneticist Dr Dean Jerry and his team have developed a technique which can extract and identify DNA from all species of tilapia in a water body just days after they arrive."

Acutally, this technique was first developed by the University of Notre Dame in the US, in collaboration with QLD Fisheries and the Invasive Pest CRC. The project was one of the many casualties of the Newman Government's war on any thing to do with the environment

Cameron Hunt - 21 Jan 2015 9:40:24pm

I live near a small freshwater creek in Cairns and I cleared out all the tilapia in a single hole by fishing them out with light line, small hooks and garden worms. They seem to continually school up and I can continue to catch every one in the whole school by floating the bait in front of their nose. I've tried different baits but they really go aggressively at the worms.

Jeff K - 07 Nov 2014 8:48:09pm

By the time you have stunned a fish when electro-fishing you have either killed or seriously injured the fish. The fish are drawn to the electrical current, so you use the current to draw the fish out, not to stun them.

Andrew - 29 Dec 2014 2:54:27pm

Sorry Jeff but you are completely misguided. Electrofishing is the safest, least harmful method of catching fish in freshwater. Stunned fish can be easily handled, weighed and measured, tagged etc., and recover within minutes to be safely released (native species). Injury and mortality rates are far lower than catching them with nets or traps, so much so that electrofishing is used to catch all broodstock in NSW govt freshwater fish breeding programs, and probably in all other states as well.